The work aims to carry out the lightweight design in the finite element method, to minimize its weight when the strength and working performance are met, with the turn frame as the research object. In view of the actual conditions of the turn frame, its weight was reduced by means of the topology optimization and size optimization. The strength of the turn frame was analyzed under the loading and extreme working conditions on the basis of meeting the working performance and the strength of turn frame. The topology optimization and size optimization of the turn frame were consecutively carried out based on the analysis results. The strengths of the turn frame before and after the optimization were compared and analyzed. After the optimization, the strength of the turn frame met the requirements, and its weight was reduced by 17%. The turn frame structure of the unloading machine designed meets the strength and working performance requirements and achieves a better lightweight effect.